Process for the absorption of nitrous gases



J. L. LA COU?.

PROCESS FOR THE ABSORPTION 0F NITRUS GASES.

APPLICATION FILED OCT. 22. 1918.

Patented Aug. l3, 192

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.L 71,0611 fr UNITED STATES PATENT OFFICE.

'TENS LASSEN LA COUR, OF CHRIS-TIANIA, NORWAY, ASSIGNOR TONORSK HYDRO ELEKTRISK KVAELSTOFAKTIESELSKAB, OF CHILESLIA'IIIA1 NORWAY.

PROCESS FOR THE BSORPTION'OF NITRQUS' GASES.

Specification of Letters Patent. p

Patented Aug. 3, 1920.

Application led October 22, 1918. Serial No, 259,294.

To all wtom t 'may concern:

Be it known that I, JENs LAssEN LA COUR, a subject of the King of Sweden, residing at Christiania, Norway, have invented certain new and useful Improvements in Processes for the Absorption of Nitrous Gases; .and I do hereby declare the following to be a full, clear, and exact description of the invention, such as will enable others skilled in thel art to which it appertains to make and use the same.

This invention relates to the absorption of nitrous gases in a cyclic system and has for its object an improved method of carrying such absorption into edect. Y f For effecting the absorption of nitrous i ases in a cyclic systemany known method may of course be employed when suitably modified. If the nitrogen oxids' however are absorbed in water or aqueous solutions the residual gases must be driedbefore they vcan be returned into the electric furnaces.

It has therefore been suggested to effect the absorption either in sulfuric acid or in dry bases. The absorption in sulfuric acid however involves several difficulties espe- .cially in the denitration of the obtained nitrosyl-sulfuric acid. On the other hand' the. absorption in dry bases produces a product of alower value. y

A third method of recovering the nitrous gases consists in strongly cooling these lat ter so as to effect the freezing out of the N2 O4 or as' gases in the form of N2 O, and a mixture of these oXids. Also this method is however connected with several draw- Aso backs. In fact very large refrigeration plants with a large expenditure of energy are required for the refrigeration of such dilute gases as are usually obtained from the electric oxidation furnaces particularly when the furnaces are working substantially under atmospheric pressure, -and notwithstanding this the residualgases leavingihe refrigeration plant will contain a considerable percentage of nitrogen compoundS, which when directly'introduced into the electric furnaces will bellost because they become decomposed into'ytheir' components.

According to the present inventionl and a s illustrated diagrammatically in the draw ing these disadvantages are avoided by freezing out the great rpart of the nitrogen compounds by coo ing` the gases down to extremely low temperatures in a ,com

denser plant C and'by absorbing the last traces of the nitrogen compounds by passing the residual gas' in Contactv with dry bases such as slaked lime in. absorption towers A, B. By working in this manner the gases then remain dry all along and can again be returned to the electric furnaces.

To enable the dry bases to 'absorb the residual gases, these latter should be heated to a rather high temperature. This is most eiliciently effected by passing the residual gases in counter current to the hot furnace gases through a preheater D (interchanger) in which the gases leaving the furnace F deliver part of their heat to the cold gases from the refrigeration plant C. On leav'n ing the absorption tower containing the dry bases 'the gas is still so hot that it without being preheated or after a slight heating in a heater E may be introduced into the flame space of the electric furnaces.

This preheater E for theA gases is suitably" constructed in direct connection with the electric furnaces F' to avoid radiation of heat from the latter. To effect the condensation of the greatest possible quantity of the nitrogen oxids and allow of constructing the refrigeration plant with its expenfrom the electric furnaces in contactwith the nitrate and then back to the absorption system, where the 'nitrogen compounds are Yfor the greater partseparatedv out .in the refrigeration. plant. This'may be carried out in the manner, that as soon as the dry basesv have been' sufliciently saturated with nitrogen compounds the absorptiontower isf disconnected from the circulation system at .a point in rear of the refrlgeration plant and connecting it directly in rear ofv the furnaces.

This can readily be done by suitable arrangement of valves or dam-pers in system-.f-

In the drawings I have dia-grammaticaily shown a plant for carrying out my process. v[ have shown two absorption towersl A and B filled with an alkaline absorptionu matethe riai, as briquets of burnt lime or slalred lime, -Byjmeans of valves or dampers V to fl-Vio these towers may be connected to or disconnected from the circulation system, as fdesired' V"When the dampers V V8, V, and 'V3 areiopen and all the others closed, gases from the electricv furnace l? pass through pipe Jy into the condensing or refrigerating apparatus C, the condensedunitrogenitetroxid N2 .Oli being drawn off at K, While the uncondensed gases pass by pipe L through the heat interchanger D to bey reheated prepara- 'ftory to absorption. These uncondensed gases pass by .'pipe L through the heat interchanger D, pipes M and S into the absorber A., The gases then pass damper l?, into pipe N and heat inter-changer E, Where they are highly heated reparatory to being forced by the blower .i back into the furnace F through the pipe P. In order to `compensate for the combined oxygen, oxygen is pumped by pump H into the pipe P leading to the furnace.

lWhen the contents of the tower- A have become saturated it is disconnected from the circulation system by closing dampers or valves V2 and V3. By opening valves VS and Vm tower B is placed in circuit.

The tower A. can now be emptied of its content of nitrates. and replenished with fresh absorption material.

The operation may also be altered, so as to decompose the nitrate in the towers.

7lWhen tower A. has been saturated, the dampers V2 V3, V, and V5 are closed, and the remaining ones open. rflue hot gases from 'furnace F pass through pipe J and damper V into the absorption chamber A, decomposing the calcium nitrate and'nitrite therein by the heat of said furnace gases. The combined gases then pass through pipe 'its bach into pipe J' and cooler C, the uncondensed gases passing by pipe L, heat interchanger l), pipe M, valve V9, and pipe T to the absorption tower B, the residual gases passing through damper V10, pipe N, heat inter-changer E, blower G and pipe l baclr to the furnace F, beni@r supplied as before with oxygen by pump y It is thus possible jto maintain@continuous Working in cyclic system described, by cans ing the towers A and to alternately actl for absorption.. 1 .i

I claim: i

1. The necesa` oifabsorbing nitrous gases,

, .1 which comprises condensing a substantial' portion of the gases .from an elect'f'ic furnace for the production of nitrogen compounds and re-heatlng the residual uncondensed nitrogen onid gases to absorbing temperature, and absorbing said gases in dry bases at a raised einperature.

2. The process of a sorbing nitrous gases,

"which comprises cool ng the gases from a nitrogen oxidation rfurnace by cold residual gases, thereby condensing a substantial pori' tion of the cooled gases, and absorbing residual nitrogen compounds of said gases in dry bases heated by the furnace gases to absorbing condition.

3. The process of recovering nitrous fur* 1 oxids in a dry base heated by the furnace gases and returning the residue of the gases from the dry base into the cycle of operations.

4. The process of recovering nitrous fury nace gases, which comprises cooling the gases by cold uncondensed furnace gases, thereby condensing a substantial portion of the cooled gases, absorbing uncondensed cold gases inl lime previously heated by the furnace gases, returning the residual gasesl into the cycle of operations and decomposing absorption products by hot furnace gases and conducting such products with furnace gases to the condensing stage.

5;' nThe process of. recovering nitrous fur. nace gases, which comprises cooling said gases, thereby condensing a substantial. proportion of their nitrogen tetroxid, heating the residual gases by cooling of the furnace gases therewith, absorbingthe heated residual gases in dry bases, heating theI gases leaving said dry bases and introducing them into the furnace and decomposing the absorption product by irncooled furnace gases and conducting the gaseous products of such decomposition with furnace gases to the cooling and condensing stage.

ln testimony that l claim the foregoing as my invention, l have signed my name in presence of two subscribing Witnesses.

y TENS LASSEN LA COUR.

I Witnesses: 

